WO2024259623A1

WO2024259623A1 - Ion-exchangeable glasses with low ai2o3-content for display devices

Info

Publication number: WO2024259623A1
Application number: PCT/CN2023/101637
Authority: WO
Inventors: Susanne Krueger; Ulrich Fotheringham; Wei Xiao; Xiaoxuan CHEN; Julia Weißhuhn
Original assignee: Schott Glass Technologies Suzhou Co Ltd; Schott AG
Current assignee: Schott Glass Technologies Suzhou Co Ltd; Schott AG
Priority date: 2023-06-21
Filing date: 2023-06-21
Publication date: 2024-12-26
Anticipated expiration: 2025-12-21
Also published as: JP2026513079A; TW202508995A; CN121399073A; EP4731585A1; KR20260015305A

Abstract

This disclosure relates to glasses and glass articles made from glasses with low Al₂O₃-content. The glass articles include flat glass suitable for use in display devices, in particular foldable dis-play devices, such as for electronic devices, including smartphones, smart watches and tablet computers. A method of making glass articles is described as well.

Description

Ion-exchangeable glasses with low Al2O3-content for display devices

Background

Display devices, in particular foldable display devices, such as smartphones and tablet comput-ers, are becoming more and more popular. Foldable devices combine the benefits of a large screen when unfolded and portable size when folded. In order for a glass sheet to be usable in such a foldable display device, it has to be extremely thin. A very thin glass is prone to break-age. Still, such a glass must be sufficiently strong to withstand repeated folding and unfolding operations.

Typically, aluminosilicate glasses were used in portable electronic devices. Aluminosilicate glass has certain properties that make it well suited for use as a display glass, especially in cases of display cover glasses which need to be flexible or foldable and have thicknesses below 100 μm. However, compressive stress diminishes in aluminosilicate glass with smaller thick-ness. Additionally, ways of further increasing the impact resistance in alkali aluminosilicates of-ten lead to an increased tendency to devitrify during production which decreases yield. Conse-quently, a solution must be found to both increase the compressive stress even for thin glasses and maintain devitrification stability. Further, it would be advantageous if such new glasses would also possess an improved acid resistance since the glass surface of touch screens may be exposed to the acidic conditions of the user’s skin.

It would be good to have a glass that overcomes the shortcomings of the prior art.

Summary of the disclosure

In a first aspect, this disclosure relates to a glass comprising the following components:

i. SiO₂,

ii. Al₂O₃ in an amount of 0.0 to 6.0%by weight,

ii. ZrO₂ in an amount of at least 8.0%by weight,

iii. Na₂O in an amount of at least 12.0%by weight,

iv. 0.0 to 5.0%by weight of B₂O₃

v. 0.0 to 5.0%by weight of Li₂O,

vi. 0.0 to 10.0%by weight of K₂O; and

vii. optionally, one or more components selected from P₂O₅ and TiO₂.

In a second aspect, this disclosure relates to a glass comprising the following components in percent by weight:

and, optionally, comprising a dye or colorant such as Fe₂O₃, CoO, and/or Cr₂O₃.

The inventors found that the glass according to the first and second aspects provides for a novel combination of desirable properties. It was found that prior art glasses have insufficient devitrification stability and impact resistance, even after chemical strengthening. Thus, to im-prove the impact resistance and maintaining devitrification stability, the glasses of this disclo-sure were developed.

In the present disclosure, an improved packing density was achieved by significantly reducing Al₂O₃ and significantly increasing the ZrO₂ content. Zirconium is octahedrally coordinated in the glass network, so that the packing density is higher than in the alkali aluminosilicates that are usually used. When Al₂O₃ is limited to < 5 wt%a production with high yields (devitrification sta-bility) is achieved. Further, due to the low working points (at least at those temperatures, at which the viscosity is equal to or less than 10⁴ dPa*s) of the alkali zirconium silicates compared to the commonly used aluminosilicates, such glasses may be produced at lower temperatures, so that both the environment is protected, and energy costs can be reduced.

Despite the rather low Al₂O₃-content, the glass has surprisingly remarkable susceptibility to chemical strengthening. This means that when immersed in a salt bath for chemical toughening, the glass will build a high compressive stress on its surface within a very short time. In an em-bodiment, this compressive stress susceptibility will be as high as 800 MPa, or even 900 MPa or even 1000 MPa or even 1100 MPa or higher within 30 minutes of chemical toughening. De-spite this remarkable susceptibility to compressive stress, the glass has only moderate thermal expansion, such as a coefficient of thermal expansion of less than 9.8 ppm/K or even less than 9.0 ppm/K. This very moderate thermal expansion allows for the production of articles with ex-cellent dimensional characteristics. During production of thin glass, for example in a down draw process, the glass will experience fast cooling. Typically, the cooling rates will not be exactly the same for all portions of the glass. This will lead to warp in the glass article. Warp will be higher for articles made of glass with higher coefficients of thermal expansion. Because the glass of this disclosure has low coefficients of thermal expansion, glass articles with particularly low warp can be produced.

Further, the glass of this disclosure also has excellent chemical resistance, in particular acid re-sistance. Chemical resistance is very useful in glass for display applications. Prior art glasses with considerable chemical strengthening characteristics usually have mediocre or insufficient chemical resistance. In one embodiment, the acid resistance class of the glass may be class 2 or better, the alkali resistance class of the glass may be class 2 or better, and the hydrolytic re-sistance class of the glass may be at least class 4 or better.

In a third aspect, this disclosure relates to a glass article comprising or consisting of a glass de-scribed herein.

In a fourth aspect, this disclosure relates to a glass article having less than 1000 μm thickness, wherein the article comprises a glass comprising SiO₂ in an amount of at least 40.0%by weight, Na₂O in an amount of at least 12.0%by weight, further comprising ZrO₂, wherein the ratio of the amount by weight of ZrO₂ to the sum of the amounts by weight of Al₂O₃ and B₂O₃ is at least 1.5, the glass having a CSS_30μm of at least 700 MPa and/or having an acid resistance of less than 5.0 mg/dm², or an acid resistance of less than 2.5 mg/dm².

In a fifth aspect, this disclosure relates to a glass article comprising or consisting of a glass de-scribed herein and comprising an ion-exchanged layer on one or both of its major surfaces.

In a sixth aspect, this disclosure relates an electronic device comprising a glass or a glass arti-cle as described herein.

In a seventh aspect, this disclosure relates to a method of making a glass, or a glass article of this disclosure.

Detailed description

Definitions

Coefficient of thermal expansion (_” CTE “) is the average coefficient of linear thermal expansion in a temperature range from 20℃ to 300℃. It is determined in accordance with DIN ISO 7991: 1987.

Compressive stress susceptibility ( “CSS” , or “CSS score” ) is given in MPa. It is the amount of compressive stress measured in a specimen of the glass under specific test conditions. For this test, the specimen may be in the form of a sheet of 200 μm or 30 μm thickness. The specimen is subjected to ion exchange treatment in an alkali nitrate salt bath (100%) for a duration of 30 minutes, wherein for small glass thicknesses (< 35 μm) the duration of chemical toughening can be reduced, e.g., to 15 minutes. The temperature may be chosen such that the highest chemi-cal stress is obtained. The alkali nitrate salt depends on the kind of ion exchange treatment to be performed, i.e., which ions need to be exchanged. Optionally, the alkali nitrate salt is KNO₃ and the bath temperature is 440℃. The fact that a specimen of 200 μm or 30 μm thickness in the form of a sheet is used to determine CSS does not mean a restriction to glass articles in sheet form, or even to sheets of that thickness. Instead, CSS is a property of the glass material that is measured on a sheet prepared from the glass. Whereas CSS is influenced by the ther-mal history of a glass, it is a feature of the glass material or glass articles. Notably, CSS is a fea-ture of the un-strengthened material or article, i.e., untreated by ion exchange. The different thicknesses that the CSS values relate to are indicated as an index, e.g., CSS_30μm for a 30 μm thick sheet.

“1000 MPa IOX-time” is the time of ion exchange treatment needed by a glass to build a com-pressive stress on its surface of at least 1000 MPa. The corresponding experiment is the same as for CSS measurement, i.e., the specimen is a 200 μm thick glass sheet immersed in an alkali nitrate bath. The temperature may be chosen at 380℃ for sodium nitrate baths, and at 440℃ for the other alkali nitrates. The “1000 MPa IOX-time” is reached when the specimen has a compressive stress of at least 1000 MPa.

Compressive stress (CS) is the induced compression of the glass network after ion exchange on the surface layer of glass. CS usually decreases from a maximum value at the surface of the glass layer (surface CS) towards the inside of the glass layer. As is customary in the art, any in-dication of CS in this disclosure relates to the maximum value of the respective surface. Com-mercially available test machines such as FSM6000LE (company ORIHARA INDUSTRIAL CO. LTD) or SLP1000 (company “ORIHARA” , Japan) can be used to measure the CS.

Depth of layer (DoL) is the thickness of the layer at the surface of a glass article where CS ex-ists, which essentially corresponds to the thickness of an ion exchanged layer. Commercially available test machines such as FSM6000 (company “Luceo Co., Ltd. ” , Japan/Tokyo) can be used to measure the DoL by a wave guide mechanism.

“Diffusivity” (D in μm²/h) is a material property of a glass that describes its ability to build an ion-exchanged layer upon chemical toughening/ion exchange. This property can be calculated by examining the depth of the ion-exchanged layer (DoL in μm) upon ion exchange after a certain ion exchange time (IET in hours) . The higher the diffusivity, the deeper the DoL after a given time of ion exchange. The corresponding formula isIn this disclosure, if nothing else is indicated, any indication of D relates to chemical toughening with an alkali nitrate salt (100%) for 30 minutes, wherein for small glass thicknesses the duration of chemical toughening can be reduced, e.g., to 15 minutes. The temperature may be chosen at 380℃ for sodium ni-trate baths, and at 440℃ for the other alkali nitrates. The alkali nitrate is the nitrate of the alkali metal ion that has the next larger diameter compared to the most abundant alkali metal oxide in the glass composition. The diameters of the alkali metal ions are Cs>K>Na>Li, e.g., if the most abundant alkali metal oxide in the glass is sodium, D is indicated for ion exchange with 100% KNO₃ at 440℃ for 30 minutes.

Central tension (CT) : When CS is induced on one side or both sides of a glass sheet, to bal-ance the stress according to the 3^rd principle of Newton’s law, a tension stress must be induced in the center region of glass, and it is called central tension. CT can be calculated from meas-ured CS and DoL.

As used herein “surface roughness” relates to the average roughness R_a, which is a measure of the texture of a surface. Commonly, amplitude parameters characterize the surface based on the vertical deviations of the roughness profile from the mean line. R_a is the arithmetic average of the absolute values of these vertical deviations. It can be determined according to DIN EN ISO 4287: 2010-07.

Warp is the difference between the maximum and minimum distances of the median surface of a free, unclamped glass article from a reference plane. The warp may be measured as de-scribed in SEMI MF1390.

The total thickness variation (TTV) is the difference between the highest thickness and the low-est thickness of a glass article. It may be measured as described in SEMI MF1530.

“Hydrolytic resistance” relates to the extracted Na₂O equivalent. It is determined in accordance with ISO 719: 2020-09. It is a measure of the extractability of the basic compounds from the glass in water at 98℃. The result of the measurement is the extracted Na₂O equivalent in μg per g of glass.

“Alkali resistance” relates to the resistance of a glass to alkaline attack. It is determined accord-ing to ISO 695: 1991-05 using a boiling aqueous solution of sodium carbonate and sodium hy-droxide. The test is performed as described under section 6.2 “glass as a material” . The result is the loss in mass per surface area of the glass sample in mg/dm².

“Acid resistance” relates to the resistance of a glass to acid attack. It is determined according to DIN 12116: 2001-03 using a boiling aqueous solution of hydrochloric acid. The test is performed as described under section 6.3 “glass as a material” . The result is the loss in mass per surface area of the glass sample in mg/dm².

“T₄” is the temperature at which the glass has a viscosity of 10⁴ dPa*s. T₄ can be measured by methods known to a person skilled in the art for determining the viscosity of glass, e.g., in ac-cordance with ISO 7884-2: 1987-12. “T₁₃” is the temperature at which the glass has a viscosity of 10¹³ dPa*s. Similarly, other temperatures indicated as T_n refer to the temperature where the glass has a viscosity of 10ⁿ dPa*s. For example, “T₅” is the temperature at which the glass has a viscosity of 10⁵ dPa*s. The “strain point” (T_14, ₅) is defined as a temperature at which all move-ment of the glass molecules has reached a point at which no more strain can be introduced into the hot glass. It is a viscosity fixed point (temperature value) at the viscosity η = 10^14.5 dPa*s.

This limit represents the highest service temperature of a glass component. “T_g” is the transfor-mation temperature according to ISO 7884-8: 1987.

Three-point bending strength is a test of the flexural strength of a material. It may be determined using the method described in ASTM C1161-13. An exemplary test setup is as follows: Cylindri-cal steel bearings of 2 mm radius; support span 16 mm; specimens of size 28*28*0.2 mm³; pre-pared according to Standard procedure 7.2.4; loading speed of 5 mm/min.

Vickers Hardness was determined using a standard Vickers indenter as specified in ASTM C 1327 (2015) . The following parameters were used: force F_n (max) = 1 N; approximation speed = 4 μm/min; loading rate 2 N/min; holding time 20 s; release rate 6 N/min.

Typically, the Vogel-Fulcher-Tammann (VFT) equation is used to calculate the temperature needed to achieve a certain viscosity of a glass (see the ISO 7884 series of standards e.g. ISO 7884-1: 1987-12, 7884-2: 1987-12; 7884-3: 1987-12; 7884-4: 1987-12) :

In the VFT equation, η is the viscosity, A and B are parameters of the material, T is the temper-ature and T₀ is the Vogel temperature. A, B and T₀ are constant for any specific glass. The indi-cation of these constants provides for a more detailed information about the viscosity behavior of a certain glass composition.

“Major surfaces” of an article are the two surfaces having the largest areas among all surfaces of the article.

When in this disclosure it is mentioned that the glasses are “free of a component” or that they do not contain a certain component, then this means that this component is only allowed to be present as an impurity in the glasses. This means that it is not added in substantial amounts. Not substantial amounts are amounts of less than 3000 ppm (by weight) , less than 2500 ppm (by weight) , less than 2000 ppm (by weight) , less than 1500 ppm (by weight) , less than 1250 ppm (by weight) , particularly less than 750 ppm (by weight) or less than 500 ppm (by weight) .

The terms “chemical toughening” and “chemical strengthening” are used interchangeably hereinunder.

Compositional aspects

It was found that within the compositional matrix of this disclosure, the disclosed compositions, ratios and sum of contents provide for an improved susceptibility to chemical strengthening, maintaining devitrification resistance, and good chemical resistance (in particular acid re-sistance) . Optionally, the glass compositions as disclosed herein may essentially consist of the listed oxides, i.e. being free of any other components not mentioned in this disclosure.

In one embodiment, the glass comprises the following components:

i. SiO₂,

ii. Al₂O₃ in an amount of 0.0 to 6.0%by weight,

ii. ZrO₂ in an amount of at least 8.0%by weight,

iii. Na₂O in an amount of at least 12.0%by weight,

iv. 0.0 to 5.0%by weight of B₂O₃

v. 0.0 to 5.0%by weight of Li₂O,

vi. 0.0 to 10.0%by weight of K₂O; and

vii. optionally, one or more components selected from P₂O₅ and TiO₂.

Optionally, the glass comprises the following components in percent by weight:

and, optionally, comprising a dye or colorant, such as Fe₂O₃, CoO, and/or Cr₂O₃.

It was found that ZrO₂ may be present in amounts of at least 8.0%by weight and Al₂O₃ should be kept below 6.0%by weight to achieve the desired CSS, devitrification and acid resistance properties.

In an embodiment, the glass comprises

In one embodiment, the ratio of the amount of ZrO₂ to the amount of Al₂O₃ in percent by weight is at least 1.5. In yet another embodiment that ratio may be at least 2, at least 3, at least 4, at least 5, at least 10, at least 20, at least 30, at least 50, at least 65, at least 75, at least 100, at least 125, or even at least 130. Optionally, this ratio may be up to 200, up to 180, up to 150, up to 125, up to 110, or up to 75. For example, this ratio may be from 1.5 to 200, from 2 to 150, from 5 to 145, from 10 to 135. This ratio may include also glasses substantially free of Al₂O₃, i.e., only comprising Al₂O₃-impurities or being completely free of Al₂O₃, wherein the ratio tends towards infinity.

In an embodiment, the ratio of the amount of Al₂O₃ to the amount of ZrO₂ in percent by weight is less than 0.5, less than 0.25, less than 0.20, less than 0.15, less than 0.10, less than 0.05, less than 0.025, or even less than 0.015. Optionally, this ratio may be at least 0.001, at least 0.0025, at least 0.005, or at least 0.0065. For example, this ratio may be from 0.001 to 0.5, from 0.0025 to 0.2, from 0.005 to 0.1, from 0.0065 to 0.025. This ratio may include also glasses substantially free of Al₂O₃, i.e., only comprising Al₂O₃-impurities or being completely free of Al₂O₃, wherein the ratio tends towards 0.0.

In certain embodiments, the sum of the contents of Al₂O₃ and ZrO₂ is from 8.0%by weight to 35.0%by weight, from 10.0%by weight to 33.0%by weight, or from 12.0%by weight to 29.0%by weight. However, the combination of both components in high proportions leads to an in-creased tendency to devitrify, so that the glass cannot be manufactured using the down draw method. Therefore, the disclosed glasses may have a very small Al₂O₃ content or are free of Al₂O₃, so that a higher proportion of ZrO₂ can be dissolved in the glass.

The glass of this disclosure may comprise ZrO_2, Al₂O₃ and B₂O₃. Thus, when also B₂O₃ is pre-sent, the ratio of the amount by weight of ZrO₂ to the sum of the amounts by weight of Al₂O₃ and B₂O₃ may be at least 1.5. In yet another embodiment that ratio may be at least 2, at least 3, at least 4, or even at least 5. Optionally, the ratio of the amount by weight of ZrO₂ in weight per-cent to the sum of the contents of Al₂O₃ and B₂O₃ in weight percent is from 1.50 to 200.00, such as from 2.00 to 180, from 2.50 to 155, from 3.65 to 145 or from 4.75 to 135. In embodiments, this ratio is at least 1.50, at least 2.00, at least 3.50, at least 4.65, or at least 5.00. This ratio may be up to 200.00, up to 180.00, up to 150.00, up to 125.00, up to 110.00, or up to 75.00. This ratio may include also glasses substantially free of Al₂O₃ and/or B₂O₃, i.e., only comprising Al₂O₃ and/or B₂O₃-impurities or being completely free of Al₂O₃ and/or B₂O₃, wherein the ratio tends towards infinity.

It is important to note that conventional ZrO₂-rich glasses in the prior art necessitate a fining step with As₂O₃ and/or Sb₂O₃. This is harmful to the environment and health. The disclosed glasses can be produced without the use of As₂O₃ and/or Sb₂O₃ and still maintain high quality. Fining of the disclosed glasses may be carried out using CeO₂, SnO₂, Cl, or SO_3, or any combi-nation thereof. In one embodiment the glasses may not need fining by fining agents. Thus, in one embodiment, the fining is carried out without the use of harmful substances, such as As₂O₃ and/or Sb₂O₃ and therefore, in one embodiment, the glass composition is free of As₂O₃ and/or Sb₂O_3. In this case the term “free of As₂O₃ and/or Sb₂O₃” refers to an amount of 100 ppm by weight or less, 50 ppm by weight or less, 25 ppm by weight or less, 20 ppm by weight or less, 10 ppm by weight or less, 5 ppm by weight or less, or even 1 ppm by weight or less.

In some embodiments, the glass is free of Li₂O_. High Li₂O contents lead to increased raw mate-rial costs, which can be avoided by the disclosed glasses.

In this disclosure, the alkali metal oxides R₂O include the oxides of lithium, sodium, potassium and cesium. In some embodiments, the glass is free of lithium, potassium and/or cesium. The alkali earth metal oxides R’ O include the oxides of magnesium, calcium, strontium and barium. In some embodiments, the glass is free of magnesium, calcium, cesium, strontium and/or bar-ium.

Hereinunder R₂O is the sum of the amounts of the alkali metal oxides and R’ O is the sum of the amounts of all alkali earth metal oxides. In some embodiments, the glass has a sum of the amounts of alkali metal oxides (R₂O) , alkali earth metal oxides (R’ O) and ZnO of not more than 35.0%by weight, not more than 34.0%by weight, or not more than 33.75%by weight. Option-ally, this sum R₂O+R’ O+ZnO is at least 19.0%by weight, at least 20.0%by weight, or at least 21.0%by weight. For example, the sum R₂O+R’ O+ZnO is from 19.0 to 35.0%by weight, from 20.0 to 34.0%by weight, or from 21.0 to 33.75%by weight.

In embodiments, the glass has a sum of the amounts of alkali earth metal oxides (R’ O) and ZnO of not more than 12.5%by weight, not more than 12.0%by weight, not more than 11.5%by weight, not more than 11.0%by weight, not more than 10.5%by weight, not more than 10.0%by weight, not more than 9.5%by weight, not more than 9.0%by weight, not more than 8.5%by weight, or not more than 8.25%by weight. Optionally, this sum R’ O+ZnO is at least 0.1%by weight, at least 0.5%by weight, at least 0.75%by weight, at least 1.0%by weight, or at least 1.9%by weight. For example, the sum R’ O+ZnO is from 0 to 12.5%by weight, from 0 to 11.5%by weight, from 0 to 10.5%by weight, from 0 to 9.5%by weight, from 0 to 8.5%by weight, from 0.1 to 11.0%by weight, from 0.5 to 10.0%by weight, from 1.0 to 9.0%by weight, from 1.5 to 8.5%by weight, or from 1.9 to 8.25%by weight.

The glass may comprise one or more alkali metal oxides (R₂O) . Optionally, a ratio of a second most abundant alkali metal oxide B, and a most abundant alkali metal oxide A in weight percent is less than 0.23, less than 0.22, less than 0.18, less than 0.16, less than 0.12, or less than 0.10. The “most abundant” alkali metal oxide is the one that has the highest proportion in the glass based on weight percentage. Accordingly, the “second most abundant” is the one having the second highest proportion on a weight percent basis and so on. In an embodiment, A is Na₂O, and B is K₂O, in an alternative embodiment B is Na₂O and A is K₂O. In certain embodi-ments, this ratio may be as low as 0.10 or less, 0.05 or less or even 0.04 or less. In some cases, this ratio may be 0.

In an embodiment, the glass composition has a ratio of the weight amount of K₂O relative to the sum of the weight amounts of Li₂O and Na₂O of less than 0.23, less than 0.22, less than 0.18, less than 0.16, less than 0.12, or less than 0.10. In certain embodiments, this ratio may be as low as 0.10 or less, 0.05 or less or even 0.04 or less. In some cases, this ratio may be 0.

In an alternative embodiment, a ratio of the weight amount of Na₂O relative to the sum of the weight amounts of Li₂O and K₂O of less than 0.23, less than 0.22, less than 0.18, less than 0.16, less than 0.12, or less than 0.10. In certain embodiments, this ratio may be as low as 0.10 or less, 0.05 or less or even 0.04 or less. In some cases, this ratio may be 0.

In an embodiment, the glass has a ratio of the weight amount of SiO₂ relative to the sum of the weight amounts of Li₂O and Na₂O of less than 4.5, optionally less than 4.25, or less than 4.0. Optionally, this ratio may be at least 2.0, at least 2.5, or at least 3.0. For example, this ratio may range from 2.0 to 4.5, from 3.0 to 4.25, or from 3.0 to 4.0. The inventors found that this ratio has a positive influence on the thermal expansion and CSS properties of the glass.

The glass contains SiO₂, optionally in amounts of at least 40.0%by weight, at least 41.0%by weight, at least 43%by weight, at least 45%by weight, or at least 48%by weight. In embodi-ments, the content of SiO₂ is up to 70.0%by weight, up to 68.0%by weight, up to 66.0%by weight or up to 64.0%by weight. In certain embodiments, the relative amount of this component is from 40.0 to 70.0%by weight, from 41.0 to 68.0%by weight, from 43.0 to 66.0%by weight or from 48.0 to 65.0%by weight. SiO₂ helps to achieve the desired thermal expansion behavior and the chemical resistance property. If the SiO₂ content is too large, viscosity increases raising the temperatures of melting and hot forming. Furthermore, SiO₂ decreases ion exchangeability and with this decreasing compressive stress at the surface.

Low Al₂O₃-amounts may be used to help achieving the desired acid resistance. However, ex-cessive Al₂O₃-contents in the disclosed glass may lead to devitrification. Thus, optionally, the amount of this component is at least 0.1 %by weight, at least 0.25%by weight, at least 0.5%by weight, at least 0.75%by weight, at least 1.25%by weight, at least 1.5%by weight, at least 1.75%by weight, or at least 1.8%by weight. In embodiments, the content of Al₂O₃ may be lim-ited to up to 5.0%by weight, up to 4.5%by weight, up to 4.0%by weight, up to 3.5%by weight, up to 3.0%by weight, up to 2.5%by weight, or up to 2.0%by weight. For example, the content of this oxide may range from 0.1 to 5.0%by weight, from 0.25 to 4.5%by weight, from 0.5 to 4.0%by weight, from 0.75 to 3.5%by weight, from 1.0 to 3.0%by weight, from 1.25 to 2.5%by weight, or from 1.5 to 2.0%by weight. However, Al₂O₃ contributes to lowering the acidic re-sistance of the glass and increases the viscosity of the glass. In addition, a glass melt with a high Al₂O₃ and high ZrO₂ content tends to devitrify, thus, Al₂O₃-amounts of more than 6.0%by weight should be avoided. In some embodiments the glass may be free of Al₂O₃.

The glass may contain B₂O₃ in proportions of up to 5.0%by weight, up to 4.5%by weight or up to 3.0%by weight. In some embodiments, the content of this component is as low as 0.75%by weight or less, 0.5%by weight or less, or even 0.25%by weight or less. Some embodiments contain less than 0.1%by weight of B₂O₃. If present, B₂O₃ helps balance any devitrification ten-dency that might arise from the use of ZrO₂. Optionally, the content of B₂O₃ ranges from 0 to 5.0%by weight, from 0 to 4.5%by weight or from 0 to 3.0%by weight. In some embodiments, B₂O₃ is used in an amount of at least 0.25%by weight, or at least 0.5%by weight. A too high proportion of B₂O₃, however, impairs chemical toughening performance, especially for short in-cubation times, thus, B₂O₃-amounts of more than 5.0%by weight should be avoided. In some embodiments the glass may be free of B₂O_3.

The glass may comprise Al₂O₃ and/or B₂O₃ in a total amount of from 0.0 to 10.0%by weight, provided that the ratio of the amount by weight of ZrO₂ to the sum of the amounts by weight of Al₂O₃ and B₂O₃ is at least 1.5. Optionally, the glass may comprise Al₂O₃ and/or B₂O₃ in a total amount of from 0.0 to 9.5%by weight, from 0.0 to 9.0%by weight, or from 0.0 to 8.5%by weight provided that the ratio of the amount by weight of ZrO₂ to the sum of the amounts by weight of Al₂O₃ and B₂O₃ is at least 1.5. In an embodiment, the sum of the contents of Al₂O₃ and B₂O₃ is less than 9.5%by weight, less than 9.0%by weight, less than 8.5%by weight, less than 8.0%by weight, or less than 7.0%by weight. Optionally, the sum of the contents of Al₂O₃ and B₂O₃ is at least 0.5%by weight, at least 0.75%by weight, at least 1.0%by weight, at least 1.25%by weight, or at least 1.5%by weight. In some embodiments the glass may be free of Al₂O₃ and B₂O_3.

P₂O₅ is an optional component. It may be used in proportions of at least 0.015%by weight, at least 0.02%by weight, at least 0.025%by weight or at least 0.03%by weight. Suitable upper limits are 10.0%by weight, 8.0%by weight, 6.0%by weight, 5.0%by weight, 4.0%by weight and 3.5%by weight. Optionally, P₂O₅ may be used in ranges from 0 to 10.0%by weight, from 0.02 to 8.0%by weight, from 0.025 to 5.0%by weight, or from 0.03 to 3.5%by weight.

Some embodiments include TiO₂ as a glass component. It may be used in amounts of from 0.0 to 5.0%by weight, from 0.0 to 4.0%by weight, from 0.0 to 3.0%by weight, from 0.0 to 2.0%by weight, from 0.0 to 1.5%by weight, from 0.0 to 1.0%by weight, or in amount of less than 100 ppm.

ZrO₂ is an important component in the glass composition. It was found that ZrO₂ should be pre-sent in amounts of at least 8.0%by weight and Al₂O₃ needs to be kept below 6.0%by weight in order to achieve the desired resistance to devitrification. Desirably, the amount of ZrO₂ is at least 8.0%by weight, at least 9.5%by weight, at least 10.0%by weight, at least 10.5%by weight, at least 11.0%by weight. In some embodiments, the amount of ZrO₂ may be at least 8.1%by weight, at least 8.5%by weight, at least 8.8%by weight, at least 9.2%by weight, or at least 9.5%by weight. In embodiments, the amount of this component ranges up to 32.0%by weight, or up to 30%by weight. Optionally, the content of ZrO₂ in the glass may range from 8.0 to 32.0%by weight, from 9.5 to 32.0%by weight, from 10.0 to 30.0%by weight, from 10.5 to 20.0%by weight, from 11.0 to 17.5%by weight, from 8.1 to 28.0%by weight, from 8.5 to 24.0%by weight, from 8.8 to 23.5%by weight, or from 9.5 to 22.5%by weight. In an embodiment, the amount of ZrO₂ is at least 8.5%by weight, at least 8.7%by weight, or at least 9.0%by weight. In certain embodiments, the amount of ZrO₂ may be at least 8.0%by weight, at least 9.0%by weight, or >10.0%by weight, such as at least 10.1%by weight. Thus, in an embodiment, the amount of ZrO₂ may range from 8.0%by weight to 30.0%by weight. ZrO₂ is an essential com-ponent to increase compressive stress at the surface after ion exchange due to increasing packing density. It further improves chemical resistance and decreases CTE. However, it was found that if ZrO₂ is too high, meltability deteriorates and devitrification as well as phase separa-tion can occur which lowers yield.

In some embodiments Y₂O₃ may be present in the glass composition. The amount of Y₂O₃ may be at least 5.0%by weight, at least 6.0%by weight, at least 7.0%by weight, or at least 8.5%by weight. In embodiments, the amount of this component ranges up to 20.0%by weight, up to 15.0%by weight, up to 10.0%by weight, or up to 5.0%by weight. Optionally, the content of Y₂O₃ in the glass may range from 0.0 to 20.0%by weight, from 0.0 to 15.0%by weight, from 0.0 to 10.0%by weight, or from 0.0 to 5.0%by weight. In some embodiments the glass may be free of Y₂O_3.

In certain embodiments, the ratio of (a) the content of ZrO₂ in weight percent to (b) the content of SiO₂ in weight percent is from 0.10 to 0.75, from 0.15 to 0.70 or from 0.19 to 0.65. In an em-bodiment, this ratio is at least 0.08, at least 0.10, at least 0.15 or at least 0.19. This ratio may range up to 0.70, up to 0.68, up to 0.65, up to 0.625, or up to 0.62.

Optionally, the glass comprises alkali metal oxides. The total amount of alkali metal oxides R₂O may be from 10.0 to 30.0%by weight. Optionally, this amount is at most 25.0%by weight, at most 23.0%by weight, at most 22.0%by weight, at most 21.0%by weight, or at most 20.5%by weight. A certain amount of alkali metal oxides may be necessary for a sufficient CSS property. Hence, a minimum amount may be 10.0%by weight, 11.0%by weight, 12.0%by weight, or even 13.0%by weight. For example, the R₂O amount may range from 10.0 to 25.0%by weight, from 11.0 to 24.0%by weight, from 11.0 to 23.0%by weight, or from 12.0 to 22.0%by weight. In certain embodiments, the sum of the contents of all alkali metal oxides R₂O is less than 20.5%by weight, less than 20.25%by weight, or less than 20.15%by weight.

Optionally, the ratio of (a) the sum of the contents of all alkali metal oxides R₂O in weight per-cent to (b) the content of SiO₂ in weight percent is from 0.1 to <0.4, from 0.15 to <0.39, from 0.2 to <0.38 or from 0.25 to <0.37.

In an embodiment, the most abundant alkali metal oxide in the glass composition is Na₂O, the second most abundant alkali metal oxide, if present, is in some embodiments K₂O, in other em-bodiments Li₂O, and the third most abundant alkali metal oxide, if present, is in some embodi-ments Li₂O, in other embodiments K₂O. Alternatively, the most abundant alkali metal oxide maybe K₂O, the second most abundant alkali metal oxide, if present, may be Na₂O, and the third most abundant alkali metal oxide, if present, may be Li₂O. In an embodiment, Li₂O is not the most abundant alkali metal oxide. Optionally, either Na₂O or K₂O is the most abundant alkali metal oxide. For example, Li₂O may be less abundant than Na₂O and/or less abundant than K₂O. Na₂O acts as network former and is an important component to ensure high compressive stress after ion exchange. It further decreases temperatures for melting and hot forming. How-ever, if Na₂O content is too high, hydrolytic resistance will decrease dramatically.

Li₂O may be present in the glass in amounts of up to 5.0%by weight, up to 3.0%by weight, up to 2.5%by weight, up to 2.25%by weight, up to 2.15%by weight, up to 2.1%by weight, up to 1.5%by weight, up to 1.0%by weight, up to 0.5%by weight, up to 0.2%by weight, or up to 0.1%by weight. High Li₂O contents increase the costs of raw material due to the increasing de-mand for Li₂O for battery production, thus, Li₂O should be kept low and Li₂O of more than 5.0%by weight should be avoided. In some embodiments, the glass may be free of Li₂O.

K₂O may be present in the glass in amounts of up to 7.0%by weight, up to 6.0%by weight, or up to 5.0%by weight. In some embodiments, the content of K₂O may be at least 4.0%by weight, or at least 3.0%by weight. In an embodiment, the glass composition comprises K₂O in an amount of 5.0%by weight or less, 4.5%by weight or less, 4.0%by weight or less, 3.5%by weight or less, 3.0%by weight or less, 2.8%by weight or less, 2.5%by weight or less, 2.0%by weight or less, or 1.5%by weight or less. It may alternatively be used in proportions of at least 1.0%by weight, at least 2.0%by weight or at least 3.0%by weight. However, too much K₂O in the glass will reduce the susceptibility to chemical toughening because the network is too open, thus, K₂O of more than 10.0%by weight should be avoided. In some embodiments, the glass may be free of K₂O.

Na₂O may be present in the glass in amounts of up to 22.0%by weight, up to 20.0%by weight, or up to 19.0%by weight. In some embodiments, the content of Na₂O may be at least 14.0%by weight, or at least 15.0%by weight.

Optionally, the total amount of Na₂O and/or K₂O may range from 10.0 to 22.0%by weight, from 14.0 to 21.0%by weight, or from 15.0 to 20.5%by weight.

A total amount of up from 10.0 to 40.0%by weight of one or more oxides selected from ZnO, Li₂O, Na₂O, K₂O, MgO, CaO, SrO, BaO, and combinations thereof, may be present in the glass. In most embodiments, this total amount will be less than 30.0%by weight, less than 25.0%by weight, or less than 22.0%by weight.

The amount of CaO in the glass may for example be at most 15.0%by weight, at most 13.5%by weight, at most 12.2%by weight, at most 6.0%by weight, at most 3.0%by weight, at most 0.5%by weight, at most 0.2%by weight, or at most 0.1%by weight. If the CaO content is too high, it can reduce susceptibility to chemical strengthening, thus, CaO amounts of more than 15.0%by weight should be avoided. The glass may also be free of CaO.

The amount of SrO in the glass may for example be at most 10.0%by weight, at most 7.0%by weight, at most 6.0%by weight, at most 5.0%by weight, at most 1.0%by weight, at most 0.5%by weight, at most 0.2%by weight, or at most 0.1%by weight. The glass may also be free of SrO.

The amount of BaO in the glass may for example be at most 10.0%by weight, at most 7.0%by weight, at most 5.0%by weight, at most 2.0%by weight, at most 1.0%by weight, at most 0.5%by weight, at most 0.2%by weight, or at most 0.1%by weight. The glass may also be free of BaO.

The sum of the amounts of CaO, SrO and BaO in the glass may for example be at most 20.0%by weight, at most 15.0%by weight, at most 13.0%by weight, at most 12.0%by weight, at most 11.0%by weight, at most 5.0%by weight, at most 2.0%by weight, or at most 1.0%by weight. In some embodiments the glass may be free of CaO, SrO and BaO.

The amount of ZnO in the glass may range from 0.0 to 5.0%by weight, from 0.0 to 4.0%by weight, from 0.0 to 3.0%by weight or from 0.0 to 2.0%by weight. Some embodiments contain less than 100 ppm of ZnO. In certain embodiments, the amount of ZnO may range from 0.5 to 5.0%by weight, or from 1.0 to 4.0%by weight. In some embodiments the glass may be free of ZnO.

The total amount of the alkali earth metal oxides plus the amount of ZnO may be 0 to 15.0%by weight, 0.0 to 10.0%by weight, 0.0 to 9.0%by weight, or 0.0 to 8.0%by weight, or 0.0 to 7.0%by weight, or 0.0 to 5.0%by weight.

Optionally, the amount of the alkali earth metal oxides R’ O is less than 10.0%by weight, less than 6.0%by weight, less than 4.0%by weight or less than 2.0%by weight. It may alternatively be used in proportions of at least 1.0%by weight, at least 2.0%by weight or at least 3.0%by weight.

In an embodiment, the ratio of (a) the sum of the contents of all alkali earth metal oxides R’ O in weight percent to (b) the content of SiO₂ in weight percent is from 0.00 to <0.06, from 0.01 to <0.3, <0.2, <0.1, <0.05 or <0.025. Optionally, this ratio may be >0.01, >0.02, or >0.03. For ex-ample, this ratio may be from >0.01 to <0.3, or from >0.02 to <0.2.

In some embodiments, the glass may contain MgO in amount of 0.0 to 9.0%by weight, from 0.1 to 8.5%by weight or from 0.5 to 8.0%by weight. Optionally, the amount of MgO is at least 0.1%by weight, at least 0.5%by weight, or at least 1.0%by weight, for example at least 1.5%by weight, at least 2.0%by weight or at least 3.0%by weight. MgO may be advantageous with re-spect to devitrification resistance. MgO also acts as network former and improves meltability. It also improves the compressive stress at the surface after ion exchange since it additionally in-creases packing density. However, if MgO content is too high, devitrification, especially due to reaction with refractive material could occur. Further, a too high MgO content could lead to phase separation. In some embodiments however, the glass is free of MgO.

Optionally, the sum of the contents of MgO and the second most abundant alkali metal oxide in weight percent is less than 10.0%by weight, less than 9.5%by weight or less than 9.0%by weight. In an embodiment, MgO may be used in proportions of at least 1.5%by weight, at least 2.0%by weight or at least 3.0%by weight. For example, the sum of the contents of MgO and CaO may be at least 1.5%by weight, at least 5.0%by weight, at least 7.5%by weight, at least 15.0%by weight, or at least 20%by weight.

An optional glass of this disclosure comprises the following components in percent by weight:

An optional boron-containing glass of this disclosure comprises the following components in percent by weight:

An optional non-boron-containing glass of this disclosure comprises the following components in percent by weight:

An optional Al₂O₃-containing glass of this disclosure comprises the following components in per-cent by weight:

An optional low Al₂O₃-containing glass of this disclosure comprises the following components in percent by weight:

An optional P₂O₅-containing glass of this disclosure comprises the following components in per-cent by weight:

An optional glass of this disclosure with relatively high K₂O comprises the following components in percent by weight:

An optional glass of this disclosure with relatively high ZrO₂ comprises the following compo-nents in percent by weight:

An optional glass of this disclosure with relatively high CaO comprises the following compo-nents in percent by weight:

An optional glass of this disclosure with relatively high MgO comprises the following compo-nents in percent by weight:

Another optional glass of this disclosure with relatively high ZrO₂ comprises the following com-ponents in percent by weight:

The glass may comprise one or more fining agents, such as CeO₂, SnO₂, Cl, SO₃. Fe₂O₃ may optionally be used as fining aid. Therefore, the glass may optionally comprise Fe₂O₃. It is desira-ble to avoid the toxic fining agent’s arsenic and antimony, so that the sum of the amounts of ar-senic and antimony may be less than 100 ppm. Due to toxicity concerns, the sum of the amounts of lead and bismuth may be less than 100 ppm. In embodiments, the glass may con-tain F in amounts of less than 1%by weight.

In one embodiment, the glass may comprise coloring ions as dyes and/or colorants, such as iron, cobalt, chromium, cupper, vanadium, nickel, manganese, neodymium, erbium, europium, molybdenum or combinations thereof. They may be used in their various oxidation states.

In one embodiment, in order to improve the meltability in this glass system further, B₂O₃, K₂O, MgO and/or CaO may be used.

Parameters

A coefficient of thermal expansion of the glass may be less than 9.8*10^-6 K^-1, less than 9.7*10^-6 K^-1 or less than 9.6*10^-6 K^-1. In exceptional embodiments the coefficient of thermal expansion is up to 10.0*10^-6 K^-1, up to 9.5*10^-6 K^-1, or up to 9.2 *10^-6 K^-1. Optionally, the coefficient of thermal expansion is at least 7.0*10^-6 K^-1, at least 7.5*10^-6 K^-1, or at least 8.0*10^-6 K^-1, or at least 8.2*10^-6 K^-1. In embodiments, the coefficient of thermal expansion of the glass ranges from 7.0*10^-6 K^-1 to 9.8*10^-6 K^-1, from 7.5*10^-6 K^-1 to 9.7*10^-6 K^-1, or from 8.0*10^-6 K^-1 to 9.6*10^-6 K^-1, or from 8.2*10^-6 K^-1 to 9.6*10^-6 K^-1. In certain embodiments, the coefficient of thermal expansion is less than 9.59*10^-6 K^-1 or even less than 9.58*10^-6 K^-1.

The glass may have a Young’s modulus of at least 74 GPa, at least 75 GPa, at least 76 GPa, or at least 77 GPa. Optionally, the Young’s modulus is up to 90 GPa, up to 88 GPa or up to 86 GPa. In embodiments, the Young’s modulus of the glass ranges from 74 GPa to 90 GPa, from 75 GPa to 88 GPa or from 76 GPa to 86 GPa. In certain embodiments, the Young’s modulus is at least 76 GPa or even at least 77 GPa. The glass of this disclosure may have an excellent Young’s modulus (in GPa) of between 70 and 90.

Generally, a higher Young’s modulus will increase the tensile stress at the glass surface upon bending. It will also reduce a glass article’s tendency to forming creases in a bending region. A high compressive stress at the surface can compensate for the tensile stress upon bending. Since the disclosed glasses show an improved susceptibility for chemical strengthening and therefore entertain a higher CSS and CS, also the Young’s modulus may be higher. This has the advantage that, especially in cases of foldable display-covers, the tendency to form creases in a bending region of the display can be reduced significantly. Thus, in one embodiment the disclosed glasses are in particular suitable for foldable display-covers.

In an embodiment, the glass has a Poisson’s ratio of from 0.220 to 0.270, from 0.225 to 0.265, of from 0.230 to 0.260. Optionally, Poisson’s ratio may be less than 0.260, less than 0.259 or less than 0.258. In embodiments, Poisson’s ratio is at least 0.220, at least 0.225 or at least 0.230.

Optionally, the glass has a density of from 2.530 to 2.850 g/cm³, from 2.580 to 2.830 g/cm³, or from 2.600 to 2.780 g/cm³. The density may be at least 2.530 g/cm³, at least 2.580 g/cm³ or at least 2.600 g/cm³. In embodiments, the density will be up to 2.850 g/cm³, up to 2.830 g/cm³, up to 2.790 g/cm³ or up to 2.780 g/cm³.

In an embodiment, the glass has a packing density of from 0.44 to 0.58, from 0.48 to 0.56, or from 0.50 to 0.54. The density may be at least 0.44, at least 0.48 or at least 0.50. In embodi-ments, the density will be up to 0.58, up to 0.56, up to 0.54 or up to 0.53.

In an embodiment, the glass may have a glass transition temperature T_g of at least 545℃, at least 550℃ or at least 555℃. In certain embodiments, T_g may even be at least 560℃ or at least 561℃, whereas particular embodiments may even have T_g values above 565℃. Option-ally, T_g may be less than 680℃, or less than 675℃. In embodiments, T_g ranges from 545℃ to 680℃, from 550℃ to 675℃, or from 553℃ to 630℃. A high T_g allows for high temperatures during ion exchange treatment. Glasses with high T_g will relax stresses induced by ion ex-change at higher temperatures less than glasses with lower T_g. Higher temperatures accelerate ion exchange processes so that ion exchange becomes more economical.

In an embodiment, the glass may have a strain point of at least 500℃, at least 525℃, at least 540℃, at least 550℃ or at least 560℃. In certain embodiments, the strain point may even be at least 543℃ or at least 573℃, whereas particular embodiments may even have strain point values above 580℃. Optionally, the strain point may be less than 700℃, or less than 675℃. In embodiments, the strain point ranges from 500℃ to 700℃, from 525℃ to 685℃, or from 540℃ to 675℃. A high strain point allows for high temperatures during ion exchange treatment. Glasses with high strain point will relax stresses induced by ion exchange at higher tempera-tures less than glasses with lower strain point. Higher temperatures accelerate ion exchange processes so that ion exchange becomes more economical.

Optionally, the glass composition exhibits one or more of

· a temperature T₄ of at least 1065℃, at least 1075℃, at least 1080℃, at least 1085℃, at least 1095℃ or at least 1100℃,

· a temperature T₃ of at least 1180℃, at least 1200℃, at least 1225℃, at least 1250℃, at least 1310℃ or at least 1330℃,

· a VFT constant A of <0.00, optionally from -5.00 to -2.00,

· a VFT constant B of >5, 000℃, optionally from 5, 800℃ to 8, 000℃, and

· a VFT constant T₀ of 140 to 450℃, such as from 145 to 300℃, or up to 255℃.

The glass of this disclosure may have remarkable steepness of the temperature viscosity curve. Steepness of the curve may be quantified as the difference between the temperatures T₄ and T_7.6. For the glass of this disclosure this difference may be at least 250 K, at least 265 K, at least 280 K, or at least 285 K. Optionally, this value does not exceed 380 K, 360 K, or 340 K. For ex-ample, the difference between the temperatures T₄ and T_7.6 may range from 250 to 380 K, from 265 to 260 K, or from 280 to 340 K.

All of these parameters describe the viscosity behavior of the glass. The glass of this disclosure has rather high characteristic temperatures, making it possible to use high temperatures during ion exchange, thereby accelerating the ion exchange process.

An important property of the glass of this disclosure is its ability to build high compressive stress in very short time. The property is quantified by a CSS score –or just “CSS” –which is equiva-lent to the compressive stress formed in a test specimen. The further used index indicates the glass thickness used for measuring CSS. The glass compositions of this disclosure have re-markable CSS values at small glass thicknesses.

Optionally, the glass of this disclosure has a CSS_200μm of at least 800 MPa, at least 950 MPa, at least 1000 MPa, at least 1050 MPa, or even at least 1070 MPa. This is a very remarkable com-pressive stress susceptibility, which allows for introduction of very high compressive stresses into the glass within short time. Optionally, CSS_200μm ranges up to 1700 MPa, up to 1500 MPa, or up to 1400 MPa. In embodiments, CSS_200μm ranges from 800 MPa to 1700 MPa, from 1000 MPa to 1500 MPa, or from 1050 MPa to 1400 MPa. Prior art glass compositions reach such high compressive stresses only after much longer ion exchange times. Often, prior art glass composition will reach compressive stresses of 1000 MPa only after more than 4 hours of ion exchange or not at all.

Optionally, the glass of this disclosure has a CSS_30μm of at least 600 MPa, at least 700 MPa, at least 800 MPa, at least 850 MPa, or even at least 900 MPa. Optionally, CSS_30μm ranges up to 1200 MPa, up to 1100 MPa, or up to 1000 MPa. In embodiments, CSS_30μm ranges from 600 MPa to 1200 MPa, from 700 MPa to 1100 MPa, or from 800 MPa to 1000 MPa. In an embodi-ment, the CSS_30μm score refers to the CSS_30μm. Prior art glass compositions do not reach such high compressive stresses at such small thicknesses.

Another way of expressing the remarkable property of this glass to accept compressive stress is the 1000 MPa IOX-time, i.e., the duration of ion exchange treatment in an alkali nitrate bath needed for the glass specimen to reach 1000 MPa of compressive stress at its surface. Option-ally, the 1000 MPa IOX-time of the glass of this disclosure is less than 60 minutes, less than 30 minutes or even less than 20 minutes. In an embodiment, the 1000 MPa IOX-time refers to the IOX-time in a potassium nitrate bath.

The remarkable ability of this glass to be chemically strengthened is further illustrated with refer-ence to its diffusivity. A high diffusivity means that the glass can receive a compressive stress layer of sufficient depth within a short time, making the production process of the glass more economical. In certain embodiments, the glass of this disclosure has a diffusivity of at least 8 μm²/h, 10 μm²/h, 12 μm²/h, 14 μm²/h, or 16 μm²/h. Optionally, this value may range up to 45 μm²/h, 40 μm²/h, or 35 μm²/h. In certain embodiments, diffusivity is from 8 to 45 μm²/h, from 9 to 40 μm²/h, or from 10 to 31 μm²/h.

The glass of this disclosure may have a chemical resistance characterized by one or more of

(a) a hydrolytic resistance value in μg/g sodium equivalent of less 320, or of less than 300, or of less than 280, or of less than 250, or of less than 225, or of less than 210;

(b) an alkali resistance value in mg/dm² weight loss of less than 25, or of less than 22, or of less than 20, or of less than 18;

(c) an acid resistance value in mg/dm² weight loss of less than 5.0, or of less than 2.5, or of less than 2.0, or less than 1.0.

Optionally, a hydrolytic resistance value in μg/g sodium equivalent may be at least 15, at least 50, or at least 100. In an embodiment, an alkali resistance value in mg/dm² weight loss of is at least 1, at least 5, or at least 8. In a further embodiment, an acid resistance value in mg/dm² weight loss of may be at least 0.1, at least 0.2, or at least 0.3.

Glasses of this disclosure exhibit remarkable compressive stress susceptibility in MPa relative to the total content of alkali metal oxides R₂O and alkali earth metal oxides R’ O in weight per-centPrior art glasses need very high amounts of alkali metal oxides or alkali earth metal oxides in order to achieve compressive stress during ion exchange. To the contrary, the compositions described herein build high compressive stress even with moderate proportions of alkali metals and alkali earth metals. Optionally, is at least 25, at least 30, at least 40, at least 50 or at least 60. In some embodiments, is at least 70, at least 80, or at least 90.Optionally, range up to 100, up to 75, or up to 50. In some embodiments, is from 25 to 100, from 30 to 75, or from 35 to 65. The unit of this parameter (MPa/wt. %) is not indicated for reasons of legibility.

In an embodiment, this disclosure relates to a glass having a CSS_200μm in MPa relative to the co-efficient of thermal expansion in a temperature range of from 20 to 300℃ in ppm/Kof at least 85, at least 100, at least 110, at least 120 or at least 130. Prior art glass compositions have the drawback of high thermal expansion, often above 9.0*10^-6 K^-1. The glass compositions of this disclosure provide for high CSS_200μm at low CTE, e.g., having afrom 100 to 250, from 110 to 220 or from 120 to 200. For example, may range up to 250, up to 220 or up to 200. The unit of this parameter (MPa*K/ppm) is not indicated for reasons of legibility.

The refractive index of a glass used for displays should not be too high to provide for limited re-flectance. Optionally, the refractive index n_d of the glass of this disclosure is less than 1.600, less than 1.550, or even less than 1.540. In certain embodiments, the refractive index ranges from 1.520 to 1.600, or from 1.530 to 1.550.

In an embodiment, the glass does not devitrify, in particular at the working point (at a viscosity of 10⁴ dPa*s) . This is useful for the glass to be producible in down draw processes. In an em- bodiment, the glass can be produced by down draw processes such as slot down-draw or over-flow fusion down draw. It is desirable that there is no devitrification at all at the working point of 10⁴ dPa*s. However, at a slightly higher viscosity, in particular at a viscosity of 10⁵ dPa*s, small crystal growth rates can be tolerated and glasses having crystal growth rates of not more than 0.5 μm/min at a viscosity of 10⁵ dPa*s are generally compatible with production by down draw.

Thus, for the purpose of this disclosure the devitrification resistance may be expressed in terms of crystal growth rate at a viscosity of 10⁵ dPa*s. The lower the crystal growth rate is, the higher is the devitrification resistance and thus the yield. The measurement of the crystallization rate is well-known. The crystallization rate is measured along the formed crystals, i.e., at their greatest extension. In particular, the crystallization rate is determined upon subjecting the glass to gradi-ent tempering (for example using a gradient furnace) .

The so-called lower devitrification temperature (LDT) is the temperature at which devitrification starts in an increasing temperature regimen. Above the liquidus temperature (also called upper devitrification temperature (UDT) ) crystals do not occur even after longer times. The values of LDT and UDT generally differ between different glasses. The terms “crystallization” and “devitri-fication” are used synonymously herein if not indicated otherwise.

If there is crystallization, it occurs at temperatures above the lower devitrification temperature (LDT) and below the upper devitrification temperature (UDT) , thus in a range between LDT and UDT. Generally, different temperatures are tested to determine the crystal growth rates at differ-ent viscosities. This also enables determining LDT and UDT as the lower limit and upper limit, respectively, of the temperature range in which crystallization occurs.

The crystal growth rate may be determined by thermally treating the glass for a time of 16 hours in a gradient furnace with increasing temperature regimen. A gradient furnace is a furnace hav-ing different heating zones, thus a furnace having areas of different temperatures. Increasing temperature regimen means that prior to be put into the furnace the temperature of the glass is lower than the temperature in any area of the furnace. Thus, the temperature of the glass is in-creased by putting it into the furnace independent of which area of the furnace the glass is put into. Hence, measurement of devitrification may be done by thermal treatment for 16 hours in a (preheated) gradient furnace that has zones of different temperatures. It is a location-based gra-dient, not a time-based gradient, because the gradient furnace is divided into locations or zones of different temperatures.

The furnace being divided into several heating zones enables testing different temperatures (and thus different viscosities) at the same time. This is a particular advantage of a gradient fur-nace. The temperatures shall be chosen such that the crystallization rate can be determined at different temperatures (and thus different viscosities) in the range between LDT and UDT. If LDT and UDT are unknown, it is useful that temperatures in a relatively large range are tested in order to enable determination of LDT and UDT. For example, the lowest temperature in the gradient furnace may be chosen such that it is about 350 K below the processing temperature (working point) of the glass. The working point corresponds to a viscosity of 10⁴ dPa*s.

As described above, the crystal growth rate at a viscosity of 10⁵ dPa*s is of relevance with re-spect to the producibility by down draw processes. Optionally, the glasses of the invention are so devitrification resistant that the crystal growth rate is at most 0.5 μm/min, at most 0.4 μm/min, at most 0.3 μm/min, at most 0.2 μm/min, at most 0.1 μm/min, at most 0.05 μm/min, at most 0.02 μm/min, or at most 0.01 μm/min at a viscosity of 10⁵ dPa*s, in particular when the glass is ther-mally treated for 16 hours in a gradient furnace with increasing temperature regimen. In an em-bodiment, no devitrification occurs at all at a viscosity of 10⁵ dPa*s. Importantly, if no devitrifica-tion occurs at all at a viscosity of 10⁵ dPa*s, a crystal growth rate at 10⁵ dPa*s cannot be deter-mined. No devitrification at a viscosity of 10⁵ dPa*s may also be expressed as a crystal growth rate of 0 μm/min.

Optionally, the crystallization rate is determined using glass grains, in particular glass grains of ca. 2 mm to 3 mm diameter. Such glass grains are put onto a carrier, such as a platinum carrier for the gradient tempering. For example, the carrier may have depressions, each for taking up a glass grain, and a hole at the bottom of each depression so that the crystallization rate can be determined microscopically. In view of the sizes of glass grains the depressions may have a di-ameter of 2 mm each and the holes may have a diameter of 0.9 mm each.

After the thermal treatment it can be determined microscopically which crystal growth rate oc-curred in which temperature range (and thus at which viscosity) . The crystal growth rate at a vis-cosity of 10⁵ dPa*s is determined based on the known correlation of temperature and viscosity. Based on the glass composition it is known which viscosity corresponds to which temperature. LDT and UDT may be determined as lower limit and upper limit, respectively, of the temperature range in which crystallization occurred. The different glass grains can easily be assigned to the different temperatures of the gradient furnace because it is known which position in the furnace has which temperature and which glass grain was located at which position in the furnace dur-ing the thermal treatment.

Toughenable article

A glass article of this disclosure may have a thickness of less than 1000 μm thickness, wherein the article comprises a glass comprising SiO₂ in an amount of at least 40.0%by weight, Na₂O in an amount of at least 12.0%by weight, further comprising ZrO₂, wherein the ratio of the amount by weight of ZrO₂ to the sum of the amounts by weight of Al₂O₃ and B₂O₃ is at least 1.5, having a CSS_30μm of at least 700 MPa and/or having an acid resistance of less than 5.0 mg/dm², or an acid resistance of less than 2.5 mg/dm².

A glass article of this disclosure may have a thickness of 1000 μm or less and comprise or con-sist of a glass as described herein. Generally, the article may be referred to as a thin glass arti-cle, or a glass sheet. It may have a thickness of less than 850 μm, less than 500 μm, less than 300 μm, less than 200 μm, or less than 100 μm. In some embodiments, the thickness may be as low as 80 μm or less, or 70 μm or less. Some articles have thicknesses of 50 μm or less, or 40 μm or less. Such thin glass articles have the property of being bendable and/or foldable. For such a flexible or foldable cover glass the desired thickness may be less than 100 μm, less than 80 μm, less than 60 μm, or less than 40 μm. In order for the article to be sufficiently impact re-sistant, a minimum thickness may be required. The minimum thickness may be at least 5 μm, at least 10 μm or at least 15 μm.

Owing to the remarkable property of having a low CTE and other desirable features, the glass article can be manufactured having a warp of less than 3.0 mm, less than 2.0 mm, or less than 1.0 mm. Generally, the glass article may be manufactured in a drawing process, wherein tem-perature differences between different portions of the glass will cause warp. Because the glass of this disclosure has a small CTE and other desirable properties, such as a good viscosity characteristic, articles with low warp may be obtained. In certain embodiments, warp is at least 5 μm, at least 10 μm, at least 100 μm, or at least 250 μm.

Optionally, the article may have a total thickness variation of less than 15 μm, less than 10 μm, less than 7 μm, or less than 5 μm. In embodiments, TTV may reach from 1 μm to 10 μm. In an embodiment, TTV is the thickness of a glass article ±10.0%, ±5.0%, or ±3.0%.

The article may have an area of at least 10 cm², at least 15 cm², or at least 20 cm². In embodi-ments, the article may have an area of less than 10000 cm², less than 1000 cm², or less than 200 cm².

The article may have, on one or both of its major surfaces, a surface roughness R_a of not more than 5.0 nm, not more than 3.0 nm or not more than 1.5 nm. Such very small roughness is ob-tainable in a down-draw process.

The article may have, on one or both of its major surfaces, a remarkable chemical resistance. The chemical resistance may be characterized as one or more of

(c) an acid resistance value in mg/dm² weight loss of less than 5.0, or of less than 2.5, or of less than 2.0, or of less than 1.0.

The glass article may have a Vickers hardness of at least 580, at least 590 or at least 600. Op-tionally, Vickers hardness ranges from 580 to 800, from 590 to 700, or from 600 to 630.

In an embodiment, the glass article has excellent three-point bending strength, exhibiting a three-point bending strength of at least 100 MPa, at least 200 MPa or at least 300 MPa. It is re-markable that such a strength can be achieved even without ion exchange strengthening. With such high strength to start with, the strength of the article after ion exchange is even more re-markable. Optionally, the three-point bending strength may range from 100 MPa to 600 MPa, from 200 MPa to 500 MPa, or from 300 MPa to 400 MPa.

Toughened article

The glass article may comprise an ion-exchanged layer on one or both of its major surfaces. An ion exchange layer imparts high strength to the glass article. Optionally, the article may have, on one or both of its major surfaces, a compressive stress of at least 500 MPa, at least 600 MPa, at least 700 MPa, or at least 800 MPa. In embodiments, the compressive stress may range up to 1800 MPa, up to 1600 MPa, up to 1500 MPa, or up to 1400 MPa. For example, compressive stress may range from 400 MPa to 1800 MPa, from 700 MPa to 1600 MPa, or from 800 MPa to 1400 MPa.

In an embodiment, the glass article has a thickness of 20 to 40 μm, such as 25 to 35 μm and has a compressive stress on one or both of its major surfaces of at least 600 MPa, at least 700 MPa, at least 800 MPa, at least 850 MPa, or at least 900 MPa.

Optionally, the glass article exhibits a DoL on one or both of its major surfaces of from 6 to 12 μm, or from 7 to 11 μm. For example, DoL may be at least 6 μm, at least 7 μm, or at least 8 μm. Alternatively, or additionally, DoL may range up to 15 μm, up to 13 μm, up to 12 μm, or up to 11 μm.

In an embodiment, DoL is from 15 to 25%of the article thickness, or from 16 to 20%of the arti-cle thickness. In embodiments, DoL is at least 15%of the article thickness, at least 16%, or at least 17%of the article thickness. DoL may be up to 33%, up to 25%, or up to 20%of the article thickness. In this context, DoL refers to the depth of one compressive stress layer. The total DoL of all compressive stress layers may be larger.

One of the astonishing properties of the article of this disclosure is that very high compressive stress can be achieved even in thin articles. In embodiments, the glass article has, on one or both of its major surfaces, a ratio of compressive stress in MPa to article thickness in μm of at least 4.0 MPa/μm, at least 5.0 MPa/μm, at least 6.0 MPa/μm or at least 10.0 MPa/μm. In em-bodiments, this value may reach up to 40.0 MPa/μm, up to 35.0 MPa/μm, or up to 30.0 MPa/μm. Optionally, the ratio of compressive stress in MPa to article thickness in μm is up to 10.0 MPa/μm, up to 8.0 MPa/μm, or up to 7.0 MPa/μm. In certain embodiments, the ratio of compressive stress in MPa to article thickness in μm ranges from 4.0 MPa/μm to 40.0 MPa/μm, from 5.0 MPa/μm to 35.0 MPa/μm, from 5.0 MPa/μm to 30.0 MPa/μm or from 10.0 MPa/μm to 29.0 MPa/μm. In a particular embodiment, this value ranges from 20.0 MPa/μm to 30.0 MPa/μm. In an embodiment, the ratio of compressive stress in MPa to article thickness is at least 20.0 MPa/μm, or at least 25.0 MPa/μm.

Optionally, the article may have, on one or both of its major surfaces, a ratio of compressive stress in MPa to depth of ion exchanged layer in μm of at least 50 MPa/μm, at least 75 MPa/μm, or at least 90 MPa/μm. In an embodiment, this value is even at least 100 MPa/μm, at least 120 MPa/μm or at least 140 MPa/μm. For example, the ratio of compressive stress in MPa to depth of ion exchanged layer in μm may range from 50 to 400 MPa/μm, from 75 to 300 MPa/μm, or from 90 to 200 MPa/μm. In certain embodiments, the ratio of compressive stress in MPa to depth of ion exchanged layer in μm is up to 400 MPa/μm, up to 300 MPa/μm or up to 200 MPa/μm.

In an embodiment, this disclosure relates to a glass article exhibiting a three-point bending strength of at least 400 MPa, at least 500 MPa or at least 600 MPa.

In an embodiment, the glass article has excellent three-point bending strength, exhibiting a three-point bending strength of at least 400 MPa, at least 500 MPa or at least 600 MPa. It is re-markable that such a strength can be achieved. Optionally, the three-point bending strength may range from 400 MPa to 1200 MPa, from 500 MPa to 1000 MPa, or from 600 MPa to 800 MPa.

Electronic device

The glass and/or the glass article may be used in an electronic device, such as a portable com-puter, smartphone, tablet computer and other handheld or wearable devices. The glass and/or glass article may be part of a display.

Thus, an electronic device according to this disclosure may comprise a glass or glass article ac-cording to this disclosure. The electronic device may comprise a display, wherein the display comprises the glass and/or glass article of this disclosure. The glass article may be a cover glass of the electronic device.

The electronic device may be a flexible and/or foldable device, such as a flexible and/or foldable smartphone or tablet computer.

Method of making

The glass may be produced by melting a batch of raw materials suitable for obtaining the com-positions of this disclosure. For example, the glass may be melted in a platinum crucible. After melting, the glass melt may be fined using one or more fining agents to remove bubbles. In-stead of using chemical fining agents, physical fining methods such as vacuum fining can be used.

In an industrial scale, glass articles may be prepared by float or down-draw processes such as slot down-draw or overflow fusion down draw methods. Slot down-draw is preferred because it allows for very small thickness.

After forming, the article may be strengthened by ion exchange (also called “chemical strength-ening” ) . Strengthening may include immersing the article in a bath of molten salt. The salt is se-lected based on the desired ion exchange process. In preferred embodiments, the salt will be an alkali salt, such as an alkali nitrate. In certain embodiments, the salt bath contains potassium nitrate, optionally, about 100%KNO₃.

Chemically strengthening a glass article by ion exchange is well known to the skilled person. The strengthening process may be done by immersing the glass article into a salt bath which contains monovalent ions to exchange with alkali ions inside the glass. The monovalent ions in the salt bath have larger radii than alkali ions inside the glass, e.g., Na⁺, K⁺, and/or Cs⁺. A com-pressive stress to the glass is built up after ion exchange due to larger ions squeezing into the glass network. After ion exchange, the strength of glass is significantly improved. In addition, the CS induced by chemical strengthening improves the bending properties of the toughened glass article and increases scratch resistance of the glass article. The typical salt used for chemical strengthening is, for example, K⁺-containing molten salt or mixtures of salts. Optional salt baths for chemical toughening are Na⁺-containing and/or K⁺-containing molten salt baths or mixtures thereof. Optional salts are NaNO₃, KNO₃, CsNO₃, NaCl, KCl, CsCl, Na₂SO₄, K₂SO₄, Cs₂SO₄, Na₂CO₃, K₂CO₃, Cs₂CO₃, and K₂Si₂O₅. Additives such as NaOH, KOH and other so-dium salts or potassium salts are also used to better control the rate of ion exchange for chemi-cal strengthening. Ion exchange may for example be done in KNO₃ at temperatures in a range of from 300℃ to 480℃ or from 340℃ to 480℃, in particular from 340℃ to 450℃ or from 390℃ to 450℃. Optionally, during ion exchange the temperature of the salt bath will be in a temperature range of from T_g-400 to T_g-100℃, or from T_g-250 to T_g-150℃.

Chemical strengthening is not limited to a single step. It can include multi steps in one or more salt baths with alkaline metal ions of various concentrations and/or different ions in the salt baths to reach better toughening performance. Thus, the chemically toughened glass article can be toughened in one step or in the course of several steps, e.g., two steps. Two-step chemical toughening is in particular applied to Li₂O-containing glasses as lithium may be exchanged for both sodium and potassium ions.

The inventors found that the glass exhibits a very fast ion exchange and achieves high com-pressive stress within short times. The time during which the article is immersed within the mol-ten salt bath at the indicated temperatures may range from 20 minutes to 12 hours, from 25 minutes to 4 hours, or from 30 minutes to 2 hours. Optionally, the time is at least 20 minutes, at least 25 minutes, or at least 30 minutes. In some embodiments, the ion exchange time is not more than 2 hours, or not more than 1 hour.

In an embodiment, the method includes:

· melting a batch of raw materials as needed to obtain a glass according to this disclosure,

· forming a glass article, such as a glass article as described herein,

· strengthening the article by ion-exchange treatment in an ion exchange bath.

Items of this disclosure

Each of the following items represents specific embodiments of glasses, glass articles, and other aspects of this disclosure, as described in detail hereinabove.

A first item relates to a glass composition, comprising

i. SiO₂,

ii. Al₂O₃ in an amount of 0.0 to 6.0%by weight,

ii. ZrO₂ in an amount of at least 8.0%by weight,

iii. Na₂O in an amount of at least 12.0%by weight,

iv. 0.0 to 5.0%by weight of B₂O₃

v. 0.0 to 5.0%by weight of Li₂O,

vi. 0.0 to 10.0%by weight of K₂O; and

vii. optionally, one or more components selected from P₂O₅ and TiO₂.

A second item relates to a glass composition comprising the following components in percent by weight:

and, optionally, comprising a dye or colorant such as Fe₂O₃, CoO, and/or Cr₂O₃ ^.

A third item relates to a glass composition comprising the following components in percent by weight:

A fourth item relates to a glass comprising the following components in percent by weight:

A fifth item relates to a glass comprising the following components in percent by weight:

A sixth item relates to a glass comprising the following components in percent by weight:

A seventh item relates to a glass comprising the following components in percent by weight:

An eighth item relates to a glass comprising the following components in percent by weight:

A nineth item relates to a glass comprising the following components in percent by weight:

A tenth item relates to a glass comprising the following components in percent by weight:

An eleventh item relates to a glass comprising the following components in percent by weight:

A twelfth item relates to a glass comprising the following components in percent by weight:

A thirteenth item relates to a glass comprising the following components in percent by weight:

A fourteenth item relates to a glass with relatively high K₂O comprising the following compo-nents in percent by weight:

A fifteenth item relates to a glass with relatively high ZrO₂ comprising the following components in percent by weight:

A sixteenth item relates to a glass with relatively high CaO comprising the following components in percent by weight:

A seventeenth item relates to a glass with relatively high MgO comprising the following compo-nents in percent by weight:

An eighteenth item relates to a glass with relatively high ZrO₂ comprising the following compo-nents in percent by weight:

A nineteenth item relates to a glass composition according to one of items 1 to 18, comprising SiO₂, ZrO₂, Al₂O₃ and B₂O₃, wherein the ratio of the amount by weight of ZrO₂ to the sum of the amounts by weight of Al₂O₃ and B₂O₃ is at least 1.5.

A twentieth item relates to a glass composition according to one of items 1 to 19, being free of As₂O₃ and/or Sb₂O₃

A twenty-first item relates to a glass composition according to one of items 1 to 20, wherein an amount, if at all present, of Al₂O₃, B₂O₃, Li₂O, K₂O, SrO, ZnO, SO₃, Fe₂O₃, TiO₂, SnO₂, and/or Cl, is less than 0.1%by weight, less than 500 ppm by weight, less than 200 ppm by weight, or less than 100 ppm by weight, or even about 0.0%by weight.

A twenty-second item relates to a glass composition according to one of items 1 to 21, having a coefficient of thermal expansion in a temperature range of from 20 to 300℃ of less than 15.0*10^-6 K^-1, less than 12.0*10^-6 K^-1, less than 10.0*10^-6 K^-1, less than 9.8*10^-6 K^-1.

A twenty-third item relates to a glass composition according to one of items 1 to 22, having a compressive stress susceptibility defined as a CSS_200μm score of at least 900 MPa.

An twenty-fourth item relates to a glass composition according to one of items 1 to 23, wherein the amount of ZrO₂ is at least 10.0%, or at least 12.0%by weight.

A twenty-fifth item relates to a glass composition according to one of items 1 to 24, wherein a ratio of the amount of ZrO₂ to the amount of Al₂O₃ in percent by weight of at least 2.0, or at least 3.0.

A twenty-sixth item relates to a glass composition according to one of items 1 to 25, having a 1000 MPa IOX-time of less than 60 minutes, or less than 30 minutes.

An twenty-seventh item relates to a glass composition according to one of items 1 to 26, having a glass transition temperature T_g of at least 540℃, at least 550℃ or at least 564℃.

A twenty-eighth item relates to a glass composition according to one of items 1 to 27, the glass having a steepness of its temperature-viscosity curve characterized by a difference between its temperatures T₄ and T_7.6 of from 260 to 350 K.

A twenty-nineth item relates to a glass composition according to one of items 1 to 28, wherein the glass has a diffusivity of at least 10 μm²/h, or at least 15 μm²/h.

A thirtieth item relates to a glass composition according to one of items 1 to 29, wherein the glass has a sum of the amounts of alkali earth metal oxides and ZnO of not more than 15.0%by weight.

A thirty-first item relates to a glass composition according to one of items 1 to 30, wherein the crystal growth rate is at most 0.5 μm/min at a viscosity of 10⁵ dPa*s, when the glass is thermally treated for 16 hours in a gradient furnace with increasing temperature regimen.

A thirty-second item relates to a glass composition according to one of items 1 to 31, wherein the DoL is between 5 and 12 μm.

A thirty-third item relates to a glass composition according to one of items 1 to 32, wherein the Young's modulus (in GPa) is between 70 and 90.

A thirty-fourth item relates to a glass composition according to one of items 1 to 33 comprising one or more fining agents, such as CeO₂, SnO₂, Cl, SO₃ or Fe₂O₃..

A thirty-fifth item relates to a glass composition according to one of items 1 to 34 having a coef-ficient of thermal expansion of the glass from 7.0*10^-6 K^-1 to 9.8*10^-6 K^-1.

A thirty-sixth item relates to a glass composition according to one of items 1 to 35 having a Young’s modulus from 74 GPa to 90 GPa.

A thirty-seventh item relates to a glass composition according to one of items 1 to 36 having a Poisson’s ratio of from 0.220 to 0.270.

A thirty-eighth item relates to a glass composition according to one of items 1 to 37 having den-sity of from 2.530 to 2.900 g/cm³.

A thirty-nineth item relates to a glass composition according to one of items 1 to 38 having packing density of from 0.44 to 0.58.

A fortieth item relates to a glass composition according to one of items 1 to 39 having a glass transition temperature T_g from 550℃ to 700℃.

A forty-first item relates to a glass composition according to one of items 1 to 40 having a strain point of at least from 550℃ to 670℃.

A forty-second item relates to a glass composition according to one of items 1 to 41 exhibiting one or more of

· a temperature T₄ of at least 960℃, at least 970℃, at least 1005℃, at least 1010℃, at least 1050℃ or at least 1070℃,

· a VFT constant A of <0.00, optionally from -5.00 to -2.00,

· a VFT constant B of >5, 000℃, optionally from 5, 800℃ to 8, 000℃, and

A forty-third item relates to a glass composition according to one of items 1 to 42, the glass hav-ing a steepness of its temperature-viscosity curve characterized by a difference between its temperatures T₄ and T_7.6 of from 200 to 400 K.

A forty-fourth item relates to a glass composition according to one of items 1 to 43, the glass having a steepness of its temperature-viscosity curve characterized by a difference between its temperatures T₄ and T_7.6 of from 250 to 380 K.

A forty-fifth item relates to a glass composition according to one of items 1 to 44 having a CSS_200μm from 800 MPa to 1700 MPa.

A forty-sixth item relates to a glass composition according to one of items 1 to 45 having a CSS_30μm from 600 MPa to 1200 MPa.

A forty-seventh item relates to a glass composition according to one of items 1 to 46 having a diffusivity from 10 to 80 μm²/h.

A forty-eighth item relates to a glass composition according to one of items 1 to 47 having a chemical resistance characterized by one or more of

(b) an alkali resistance value in mg/dm² weight loss of less than 25, or of less than 22, or of less than 20, of less than 18;

(c) an acid resistance value in mg/dm² weight loss of less than 5.0, or of less than 2.5, or of less than 1.0.

A forty-nineth item relates to a glass composition according to one of items 1 to 48 having com-pressive stress susceptibility in MPa relative to the total content of alkali metal oxides R₂O and alkali earth metal oxides R’ O in weight percentfrom 25 to 100.

A fiftieth item relates to a glass composition according to one of items 1 to 49 having a CSS_200μm in MPa relative to the coefficient of thermal expansion in a temperature range of from 20 to 300℃ in ppm/Kfrom 100 to 250.

A fifty-first item relates to a glass composition according to one of items 1 to 50 having a refrac-tive index n_d from 1.520 to 1.600.

A fifty-second item relates to a glass composition according to one of items 1 to 51 having no devitrification at all at the working point of 10⁴ dPa*s.

A fifty-third item relates to a glass composition according to one of items 1 to 52 having a crystal growth rate at a viscosity of 10⁵ dPa*s of at most 0.5 μm/min.

A fifty-fourth item relates to a glass comprising:

A fifty-fifth item relates to a glass composition according to item 54, having a CTE from 8.0 ppm/K to 9.0 ppm/K; or about 8.8 ppm/K.

A fifty-sixth item relates to a glass composition according to item 54, or item 55, having a Young’s modulus from 70 GPa to 85 GPa, or about 78 GPa.

A fifty-seventh item relates to a glass composition according to item 54, or one of items 55 to 56, having a Poisson constant from 0.245 to 0.255, or about 0.250.

A fifty-eighth item relates to a glass composition according to item 54, or one of items 55 to 57, having a T_g from 600℃ to 625℃, or about 611℃.

A fifty-ninth item relates to a glass composition according to item 54, or one of items 55 to 58, having a density from 2.600 g/cm³ to 2.725 g/cm³, or about 2.644 g/cm³.

A sixtieth item relates to a glass composition according to item 54, or one of items 55 to 59, having a packing density from 0.440 to 0.580, or from 0.50 to 0.54.

A sixty-first item relates to a glass composition according to item 54, or one of items 55 to 60, having a VFT A from -3.200 to -3.450, or about -3.375.

A sixty-second item relates to a glass composition according to item 54, or one of items 55 to 61, having a VFT B from 6700℃ to 6850℃, or about 6776℃.

A sixty-third item relates to a glass composition according to item 54, or one of items 55 to 62, having a VFT T₀ from 200℃ to 250℃, or about 213℃.

A sixty-fourth item relates to a glass composition according to item 54, or one of items 55 to 63, having a T_14.5 from 580℃ to 600℃, or about 593℃.

A sixty-fifth item relates to a glass composition according to item 54, or one of items 55 to 64, having a T₁₃ from 615℃ to 640℃, or about 627℃.

A sixty-sixth item relates to a glass composition according to item 54, or one of items 55 to 65, having a T_7.6. from 815℃ to 845℃, or about 831℃.

A sixty-seventh item relates to a glass composition according to item 54, or one of items 55 to 66, having a T₄ from 1100℃ to 1200℃, or about 1132℃.

A sixty-eighth item relates to a glass composition according to item 54, or one of items 55 to 67, having a T₃ from 1200℃ to 1300℃, or about 1276℃.

A sixty-ninth item relates to a glass composition according to item 54, or one of items 55 to 68, having a T₂ from 1400℃ to 1500℃, or about 1474℃.

A seventieth item relates to a glass composition according to one of items 54 to 69 having a CSS_200μm from 800 MPa to 1700 MPa.

A seventy-first item relates to a glass composition according to one of items 54 to 70 having a CSS_30μm from 600 MPa to 1200 MPa.

A seventy-second item relates to a glass composition according to one of items 54 to 71 having a diffusivity from 10 to 80 μm²/h.

A seventy-third item relates to a glass composition according to one of items 54 to 72 having a chemical resistance characterized by one or more of

(a) a hydrolytic resistance value in μg/g sodium equivalent of less than 210;

(b) an alkali resistance value in mg/dm² weight loss of less than 18;

(c) an acid resistance value in mg/dm² weight loss of less than 2.5, or of less than 1.0.

A seventy-fourth item relates to a glass composition according to one of items 54 to 73 having compressive stress susceptibility in MPa relative to the total content of alkali metal oxides R₂O and alkali earth metal oxides R’ O in weight percentfrom 25 to 100.

A seventy-fifth item relates to a glass composition according to one of items 54 to 74 having a CSS_200μm in MPa relative to the coefficient of thermal expansion in a temperature range of from 20 to 300℃ in ppm/Kfrom 100 to 250.

A seventy-sixth item relates to a glass article comprising the glass composition according to one of items 1 to 75, having a thickness of less than 1000 μm, less than 100 μm, less than 80 μm, or less than 60 μm, or less than 40 μm.

A seventy-seventh item relates to a glass article, optionally comprising the glass composition according to one of items 1 to 75, the article having less than 1000 μm thickness, wherein the article comprises a glass comprising SiO₂ in an amount of at least 40.0%by weight, Na₂O in an amount of at least 12.0%by weight, further comprising ZrO₂, wherein the ratio of the amount by weight of ZrO₂ to the sum of amounts by weight of Al₂O₃ and B₂O₃ is at least 1.5, the glass hav-ing a CSS_30μm of at least 700 MPa, and/or having an acid resistance of less than 5.0 mg/dm² or of less than 2.5 mg/dm²

A seventy-eighth item relates to a glass article according to item 76 or 77, comprising an ion ex-changed layer on one or both of its major surfaces, comprising a compressive stress of at least 400 MPa, at least 700 MPa, or at least 800 MPa.

A seventy-ninth item relates to a glass article according to one of items 76 to 78, having on one or both of its major surfaces, a ratio of compressive stress in MPa to article thickness in μm of at least 4.0 MPa/μm, at least 5.0 MPa/μm, or at least 10.0 MPa/μm, or at least 20.0 MPa/μm.

An eightieth item relates to a glass article according to one of items 76 to 79, a ratio of compres-sive stress in MPa to depth of ion exchanged layer in μm of at least 50 MPa/μm, at least 75 MPa/μm, or at least 90 MPa/μm.

An eighty-first item relates to a glass article according to one of items 76 to 80, having a thick-ness of 1000 μm or less.

An eighty-second item relates to a glass article according to one of items 76 to 81, having a warp of less than 3.0 mm.

An eighty-third item relates to a glass article according to one of items 76 to 82, having a total thickness variation of less than 15.0 μm.

An eighty-fourth item relates to a glass article according to one of items 76 to 83, having a sur-face roughness R_a of not more than 5.0 nm.

An eighty-fifth item relates to a glass article according to one of items 76 to 84, having a remark-able chemical resistance characterized as one or more of

An eighty-sixth item relates to a glass article according to one of items 76 to 85, having a Vick-ers hardness of at least 580.

An eighty-seventh item relates to a glass article according to one of items 76 to 86, having three-point bending strength from 300 MPa to 400 MPa.

An eighty-eighth item relates to a glass article according to one of items 76 to 87, having com-pressive stress of at least 400 MPa.

An eighty-ninth item relates to a glass article according to one of items 76 to 88, having a thick-ness of 20 to 40 μm.

A ninetieth item relates to a glass article according to one of items 76 to 89, having a DoL on one or both of its major surfaces of from 6 to 11 μm.

A ninety-first item relates to a glass article according to one of items 76 to 90, having a DoL from 15 to 25%of the article thickness.

A ninety-second item relates to a glass article according to one of items 76 to 91, having a ratio of compressive stress in MPa to article thickness in μm of at least 4.0 MPa/μm.

A ninety-third item relates to a glass article according to one of items 76 to 92, having on one or both of its major surfaces a ratio of compressive stress in MPa to depth of ion exchanged layer in μm of at least 50.

A ninety-fourth item relates to a glass article according to one of items 76 to 93, having a three-point bending strength of at least 400 MPa.

A ninety-fifth item relates to an electronic device comprising a glass composition according to one of items 1 to 75, and/or the glass article according to one of items 76 to 94.

Examples

Exemplary compositions of glasses according to this invention were prepared by melting appro-priate glass raw materials. The following table provides an overview of compositions and prop-erties of these glasses. Please note that the values in the tables have been rounded to one dec-imal place. Small rounding errors may therefore have occurred in the derivations and sums of the values.

1. Compositions examined

Table 1

Table 2

Table 3

The packing density was determined by dividing the ionic volume by the molar volume of the glass, wherein the ionic volume is the volume taken by one mol of the ions that make up the glass, and wherein the molar volume is the quotient of the molar weight and the measured den-sity of the glass. For calculations of the volume of each type of ion, the effective ionic radii ac-cording to Shannon are employed with coordination numbers calculated using Pauling’s rules.

2. Ion exchange treatment

Thin sheets of glass were prepared from compositions1 to 7. The sheet thickness was 200 μm. Subsequently, the sheets were ion exchange treated in a 100%KNO₃ salt bath at 440 ℃ for 30 minutes. The resulting compressive stress and depth of the ion exchanged layer (DoL) are listed in the following table.

Table 4

3. Chemical resistance

Chemical resistance was tested for glass No. 2. Hydrolytic resistance was tested according to ISO 719. Alkali resistance was measured according to ISO 695, and acid resistance was tested in accordance with DIN 12116. The results are:

· hydrolytic resistance [μg/g] : 172,

· alkali resistance [mg/dm²] : 15,

· acid resistance [mg/dm²] : 0.7.

4. Devitrification

The devitrification resistance was determined in terms of crystal growth rate (in μm/min) at a vis-cosity of 10⁵ dPa*s for compositions 1, 2, 3 and 7. The lower the crystal growth rate is, the higher is the devitrification resistance. The measurement of the crystal growth rate is well known. The crystal growth rate is measured along the formed crystals, i.e., at their greatest ex-tension.

Briefly, the crystal growth rate was determined by thermally treating the glass for 16 hours in a gradient furnace with increasing temperature regimen. Importantly, if no devitrification occurs at all at a viscosity of 10⁵ dPa*s, a crystal growth rate at 10⁵ dPa*s cannot be determined. No de-vitrification may also be expressed as a crystal growth rate of 0 μm/min at 10⁵ dPa*s.

The crystallization rate was determined using glass grains of ca. 2 mm to 3 mm diameter. The glass grains were put onto a platinum carrier for the gradient tempering. The carrier had depres-sions, each for taking up a glass grain, and a hole at the bottom of each depression for optical inspection so that the crystal growth rate was determined microscopically. The depressions had a diameter of 2 mm each and the holes had a diameter of 0.9 mm each.

The results are shown in the following table.

Claims

A glass comprising the following components:

i. SiO₂,

ii. Al₂O₃ in an amount of 0.0 to 6.0%by weight,

ii. ZrO₂ in an amount of at least 8.0%by weight,

iii. Na₂O in an amount of at least 12.0%by weight,

iv. 0.0 to 5.0%by weight of B₂O₃

v. 0.0 to 5.0%by weight of Li₂O,

vi. 0.0 to 10.0%by weight of K₂O; and

vii. optionally, one or more components selected from P₂O₅ and TiO₂.
A glass according to claim 1, comprising the following components in percent by weight:

and, optionally, comprising dyes or colorants, such as Fe₂O₃, CoO, and/or Cr₂O₃.
Glass according to one of the preceding claims, being free of As₂O₃ and/or Sb₂O₃.
Glass according to one of the preceding claims, having a coefficient of thermal expansion in a temperature range of from 20 to 300℃ of less than 15.0*10^-6 K^-1, less than 12.0*10^-6 K^-1, less than 10.0*10^-6 K^-1, less than 9.8*10^-6 K^-1.
Glass according to one of the preceding claims, having a compressive stress susceptibility defined as a CSS_30μm score of at least 700 MPa.
Glass according to one of the preceding claims, wherein the amount of ZrO₂ is >10.0%by weight.
Glass according to one of the preceding claims, wherein a ratio of the amount of ZrO₂ to the amount of Al₂O₃ in percent by weight is at least 1.5, or at least 2.0.
Glass according to one of the preceding claims, having a 1000 MPa IOX-time of less than 60 minutes.
Glass according to one or more of the preceding claims, having a glass transition tempera-ture T_g of at least 540℃, at least 550℃ or at least 560℃.
Glass according to one or more of the preceding claims, the glass having a steepness of its temperature-viscosity curve characterized by a difference between its temperatures T₄ and T_7.6 of from 250 to 350 K.
Glass according to one or more of the preceding claims, wherein the glass has a diffusivity of at least 8 μm²/h, or at least 10 μm²/h.
Glass according to one or more of the preceding claims, wherein the acid resistance value in mg/dm² weight loss is less than 5.0.
Glass according to one or more of the preceding claims, wherein the crystal growth rate is at most 0.5 μm/min at a viscosity of 10⁵ dPa*s, when the glass is thermally treated for 16 hours in a gradient furnace with increasing temperature regimen.
Glass according to one or more of the preceding claims, wherein the Young's modulus is between 70 and 90 GPa.
A glass article, optionally a glass according to one of claims 1 to 15, having less than 1000 μm thickness, wherein the article comprises a glass comprising SiO₂ in an amount of at least 40.0%by weight, Na₂O in an amount of at least 12.0%by weight, further comprising ZrO₂, wherein the ratio of the amount by weight of ZrO₂ to the sum of the amounts by weight of Al₂O₃ and B₂O₃ is at least 1.5, the glass having a CSS_30μm of at least 700 MPa and/or having an acid resistance of less than 5.0 mg/dm², or an acid resistance of less than 2.5 mg/dm².
Glass article according to claim 15, having a thickness of less than 100 μm, less than 80 μm, less than 60 μm, or less than 40 μm.
Glass article according to at least one of claims 15 to 16 comprising an ion exchanged layer on one or both of its major surfaces.
Glass article according to claim 17, having on the one or both of its major surfaces, a com-pressive stress of at least 400 MPa, at least 700 MPa, or at least 800 MPa.
Glass article according to claim 17 or 18, having on the one or both of its major surfaces, a ratio of compressive stress in MPa to article thickness in μm of at least 4.0 MPa/μm, at least 5.0 MPa/μm, at least 10.0 MPa/μm, at least 15.0 MPa/μm, or at least 20.0 MPa/μm.
Glass article according to at least one of claims 17 to 19, having, on the one or both of its major surfaces, a ratio of compressive stress in MPa to depth of ion exchanged layer in μm of at least 50 MPa/μm, at least 75 MPa/μm, or at least 90 MPa/μm.
An electronic device comprising a glass according to any one of claims 1 to 14, and/or a glass article according to one of claim 15 to 20.